On 25/07/2023 22.58, Willem de Bruijn wrote:
Stanislav Fomichev wrote:
This change actually defines the (initial) metadata layout
that should be used by AF_XDP userspace (xsk_tx_metadata).
The first field is flags which requests appropriate offloads,
followed by the offload-specific fields. The supported per-device
offloads are exported via netlink (new xsk-flags).
The offloads themselves are still implemented in a bit of a
framework-y fashion that's left from my initial kfunc attempt.
I'm introducing new xsk_tx_metadata_ops which drivers are
supposed to implement. The drivers are also supposed
to call xsk_tx_metadata_request/xsk_tx_metadata_complete in
the right places. Since xsk_tx_metadata_{request,_complete}
are static inline, we don't incur any extra overhead doing
indirect calls.
The benefit of this scheme is as follows:
- keeps all metadata layout parsing away from driver code
- makes it easy to grep and see which drivers implement what
- don't need any extra flags to maintain to keep track of that
offloads are implemented; if the callback is implemented - the offload
is supported (used by netlink reporting code)
Two offloads are defined right now:
1. XDP_TX_METADATA_CHECKSUM: skb-style csum_start+csum_offset
2. XDP_TX_METADATA_TIMESTAMP: writes TX timestamp back into metadata
area upon completion (tx_timestamp field)
The offloads are also implemented for copy mode:
1. Extra XDP_TX_METADATA_CHECKSUM_SW to trigger skb_checksum_help; this
might be useful as a reference implementation and for testing
2. XDP_TX_METADATA_TIMESTAMP writes SW timestamp from the skb
destructor (note I'm reusing hwtstamps to pass metadata pointer)
The struct is forward-compatible and can be extended in the future
by appending more fields.
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
---
Documentation/netlink/specs/netdev.yaml | 19 ++++++++
include/linux/netdevice.h | 27 +++++++++++
include/linux/skbuff.h | 5 ++-
include/net/xdp_sock.h | 60 +++++++++++++++++++++++++
include/net/xdp_sock_drv.h | 13 ++++++
include/uapi/linux/if_xdp.h | 35 +++++++++++++++
include/uapi/linux/netdev.h | 15 +++++++
net/core/netdev-genl.c | 12 ++++-
net/xdp/xsk.c | 38 ++++++++++++++++
net/xdp/xsk_queue.h | 2 +-
tools/include/uapi/linux/if_xdp.h | 50 ++++++++++++++++++---
11 files changed, 268 insertions(+), 8 deletions(-)
diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
index e41015310a6e..bf9c1cc32614 100644
--- a/Documentation/netlink/specs/netdev.yaml
+++ b/Documentation/netlink/specs/netdev.yaml
@@ -42,6 +42,19 @@ name: netdev
doc:
This feature informs if netdev implements non-linear XDP buffer
support in ndo_xdp_xmit callback.
+ -
+ type: flags
+ name: xsk-flags
+ render-max: true
+ entries:
+ -
+ name: tx-timestamp
+ doc:
+ HW timestamping egress packets is supported by the driver.
+ -
+ name: tx-checksum
+ doc:
+ L3 checksum HW offload is supported by the driver.
attribute-sets:
-
@@ -68,6 +81,12 @@ name: netdev
type: u32
checks:
min: 1
+ -
+ name: xsk-features
+ doc: Bitmask of enabled AF_XDP features.
+ type: u64
+ enum: xsk-flags
+ enum-as-flags: true
operations:
list:
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 11652e464f5d..8b40c80557aa 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1660,6 +1660,31 @@ struct xdp_metadata_ops {
enum xdp_rss_hash_type *rss_type);
};
+/*
+ * This structure defines the AF_XDP TX metadata hooks for network devices.
+ * The following hooks can be defined; unless noted otherwise, they are
+ * optional and can be filled with a null pointer.
+ *
+ * int (*tmo_request_timestamp)(void *priv)
+ * This function is called when AF_XDP frame requested egress timestamp.
+ *
+ * int (*tmo_fill_timestamp)(void *priv)
+ * This function is called when AF_XDP frame, that had requested
+ * egress timestamp, received a completion. The hook needs to return
+ * the actual HW timestamp.
+ *
+ * int (*tmo_request_timestamp)(u16 csum_start, u16 csum_offset, void *priv)
typo: tmo_request_checksum
+ * This function is called when AF_XDP frame requested HW checksum
+ * offload. csum_start indicates position where checksumming should start.
+ * csum_offset indicates position where checksum should be stored.
+ *
+ */
+struct xsk_tx_metadata_ops {
+ void (*tmo_request_timestamp)(void *priv);
+ u64 (*tmo_fill_timestamp)(void *priv);
+ void (*tmo_request_checksum)(u16 csum_start, u16 csum_offset, void *priv);
+};
+
/**
* enum netdev_priv_flags - &struct net_device priv_flags
*
@@ -1844,6 +1869,7 @@ enum netdev_ml_priv_type {
* @netdev_ops: Includes several pointers to callbacks,
* if one wants to override the ndo_*() functions
* @xdp_metadata_ops: Includes pointers to XDP metadata callbacks.
+ * @xsk_tx_metadata_ops: Includes pointers to AF_XDP TX metadata callbacks.
* @ethtool_ops: Management operations
* @l3mdev_ops: Layer 3 master device operations
* @ndisc_ops: Includes callbacks for different IPv6 neighbour
@@ -2100,6 +2126,7 @@ struct net_device {
unsigned long long priv_flags;
const struct net_device_ops *netdev_ops;
const struct xdp_metadata_ops *xdp_metadata_ops;
+ const struct xsk_tx_metadata_ops *xsk_tx_metadata_ops;
int ifindex;
unsigned short gflags;
unsigned short hard_header_len;
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index faaba050f843..5febc1a5131e 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -581,7 +581,10 @@ struct skb_shared_info {
/* Warning: this field is not always filled in (UFO)! */
unsigned short gso_segs;
struct sk_buff *frag_list;
- struct skb_shared_hwtstamps hwtstamps;
+ union {
+ struct skb_shared_hwtstamps hwtstamps;
+ struct xsk_tx_metadata *xsk_meta;
+ };
unsigned int gso_type;
u32 tskey;
diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index 467b9fb56827..288fa58c4665 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -90,6 +90,54 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp);
void __xsk_map_flush(void);
+/**
+ * xsk_tx_metadata_request - Evaluate AF_XDP TX metadata at submission
+ * and call appropriate xsk_tx_metadata_ops operation.
+ * @meta: pointer to AF_XDP metadata area
+ * @ops: pointer to struct xsk_tx_metadata_ops
+ * @priv: pointer to driver-private aread
+ *
+ * This function should be called by the networking device when
+ * it prepares AF_XDP egress packet.
+ */
+static inline void xsk_tx_metadata_request(const struct xsk_tx_metadata *meta,
+ const struct xsk_tx_metadata_ops *ops,
+ void *priv)
+{
+ if (!meta)
+ return;
+
+ if (ops->tmo_request_timestamp)
+ if (meta->flags & XDP_TX_METADATA_TIMESTAMP)
+ ops->tmo_request_timestamp(priv);
+
+ if (ops->tmo_request_checksum)
+ if (meta->flags & XDP_TX_METADATA_CHECKSUM)
+ ops->tmo_request_checksum(meta->csum_start, meta->csum_offset, priv);
+}
Might be cheaper to test the flag in the hot cacheline before
dereferencing ops?
I was thinking the same thing, but I was wrong, see below, as these ops
deref's are optimized out by the compiler.
Also, just add these functions to net_device_ops directly,
rather than dereferencing another pointer to xsk_tx_metadata_ops?
After the ASM/objdump discussion[1] in this thread, I think Stanislav's
code approach here is actually optimal. Because when the 'const' ops are
defined locally in the same file that use/does the inlining of
xsk_tx_metadata_request() then the compilers (both llvm and gcc) are
smart enough to inline and do dead-code elimination. E.g. I noticed
that generated ASM code eliminated `if (ops->tmo_request_timestamp)`
code path in mlx5 as its not implemented.
[1]
https://lore.kernel.org/all/cce9db50-8c9d-ea97-cb88-171fa46cc064@xxxxxxxxxx/
--Jesper
